A number of microorganisms having beneficial effects on plant growth and health are known to be present in the soil, to live in association with plants specifically in the root zone (Plant Growth Promoting Rhizobacteria “PGPR”), or to reside as endophytes within the plant. Their beneficial plant growth promoting properties include nitrogen fixation, iron chelation, phosphate solubilization, inhibition of non-beneficial microrganisms, resistance to pests, Induced Systemic Resistance (ISR), Systemic Acquired Resistance (SAR), decomposition of plant material in soil to increase useful soil organic matter, and synthesis of phytohormones such as indole-acetic acid (IAA), acetoin and 2,3-butanediol that stimulate plant growth, development and responses to environmental stresses such as drought. In addition, these microorganisms can interfere with a plant's ethylene stress response by breaking down the precursor molecule, 1-aminocyclopropane-1-carboxylate (ACC), thereby stimulating plant growth and slowing fruit ripening. These beneficial microorganisms can improve soil quality, plant growth, yield, and quality of crops. Various microorganisms exhibit biological activity such as to be useful to control plant diseases. Such biopesticides (living organisms and the compounds naturally produced by these organisms) are safer and more biodegradable than synthetic fertilizers and pesticides.
Fungal phytopathogens, including but not limited to Botrytis spp. (e.g. Botrytis cinerea), Fusarium spp. (e.g. F. oxysporum and F. graminearum), Rhizoctonia spp. (e.g. R. solani), Magnaporthe spp., Mycosphaerella spp., Puccinia spp. (e.g. P. recondita), Phytopthora spp. and Phakopsora spp. (e.g. P. pachyrhizi), are one type of plant pest that can cause servere economic losses in the agricultural and horticultural industries. Chemical agents can be used to control fungal phytopathogens, but the use of chemical agents suffers from disadvantages including high cost, lack of efficacy, emergence of resistant strains of the fungi, and undesirable environmental impacts. In addition, such chemical treatments tend to be indiscriminant and may adversely affect beneficial bacteria, fungi, and arthropods in addition to the plant pathogen at which the treatments are targeted. A second type of plant pest are bacterial pathogens, including but not limited to Erwinia spp. (such as Erwinia chrysanthemi), Pantoea spp. (such as P. citrea), Xanthomonas (e.g. Xanthomonas campestris), Pseudomonas spp. (such as P. syringae) and Ralstonia spp. (such as R. soleacearum) that cause servere economic losses in the agricultural and horticultural industries. Similar to pathogenic fungi, the use of chemical agents to treat these bacterial pathogens suffers from disadvantages. Viruses and virus-like organisms comprise a third type of plant disease-causing agent that is hard to control, but to which bacterial microorganisms can provide resistance in plants via induced systemic resistance (ISR). Thus, microorganisms that can be applied as biofertilizer and/or biopesticide to control pathogenic fungi, viruses, and bacteria are desirable and in high demand to improve agricultural sustainability. A final type of plant pathogen includes plant pathogenic nematodes and insects, which can cause severe damage and loss of plants.
Some members of the species Bacillus have been reported as biocontrol strains, and some have been applied in commercial products (Joseph W. Kloepper, et al. 2004, Phytopathology Vol. 94, No. 11, 1259-1266). For example, strains currently being used in commercial biocontrol products include: Bacillus pumilus strain QST2808, used as active ingredient in SONATA and BALLAD-PLUS, produced by BAYER CROP SCIENCE; Bacillus pumilus strain GB34, used as active ingredient in YIELDSHIELD, produced by BAYER CROP SCIENCE; Bacillus subtilis strain QST713, used as the active ingredient of SERENADE, produced by BAYER CROP SCIENCE; Bacillus subtilis strain GBO3, used as the active ingredient in KODIAK and SYSTEM3, produced by HELENA CHEMICAL COMPANY. Various strains of Bacillus thuringiensis and Bacillus firmus have been applied as biocontrol agents against nematodes and vector insects and these strains serve as the basis of numerous commercially available biocontrol products, including NORTICA and PONCHO-VOTIVO, produced by BAYER CROP SCIENCE. In addition, Bacillus strains currently being used in commercial biostimulant products include: Bacillus amyloliquefaciens strain FZB42 used as the active ingredient in RHIZOVITAL 42, produced by ABiTEP GmbH, as well as various other Bacillus subtilus species that are included as whole cells including their fermentation extract in biostimulant products, such as FULZYME produced by JHBiotech Inc.
The presently disclosed subject matter provides microbial compositions and methods for their use in benefiting plant growth and treating plant disease.